The families of three college students stabbed to death by a 22-year-old before he gunned down three more victims said the U.S. health and legal systems valued the rights of the mentally ill over those who become their victims.

Police said Elliot Rodger, the son of a film director, stabbed the students in his apartment on May 23, before shooting and killing three more victims in the town of Isla Vista near the campus of the University of California at Santa Barbara. He then shot himself.

"The system is clearly broken. It should have protected our sons, who were so innocent and trusting," Henry Hong, the father of Cheng Yuan "James" Hong, one of the victims, told the Washington Post in a joint interview with other victims' parents published on Thursday.

The parents are also angered over a lack of information released to them by police, by what they characterize as several missed opportunities for authorities to intervene, and expressed incredulity that Rodger could have overpowered their sons by himself, the newspaper reported.

The Santa Barbara County Sheriff's Department said in a statement it "owes it to the victim's families and to the public to not prematurely release information before we have all of the facts in this case."

Police officers had visited Rodger just weeks before the killing spree, following a concerned call from a county mental health worker, and asked him about disturbing videos he had posted online. However, they did not check the videos or look for weapons, concluding after a ten-minute meeting he was not an immediate threat to himself or others.

Rodger later wrote a lengthy manifesto that he sent to his parents, therapist and several others, minutes before launching his shooting spree. In it he said that he was afraid the police would disrupt his plot during that encounter.

Rodger was seen by a variety of healthcare professionals, according to the county sheriff.

"They knew he had problems. Why couldn't they do more?" said Kelly Wang, the mother of George Chen, according to the Post. The third victim was David Wang.